The Deal

• $99 for one professional driveway power-washing service (a $200 value)
• For a driveway up to 1,000 square feet

A wave of a pressure-washer wand can whisk away hard-to-clean grime from outdoor surfaces. Peek inside with Groupon’s look at pressure washers.

Pressure Washers: Wondrous Waterpower 

Applying pressure of up to thousands of pounds per square inch, the powerful spray from a pressure-washer’s nozzle can gently scrub siding, scour mildew off deck slats, or even strip paint. This vast power stems from three major components.

The motor: The motors of professional pressure washers are usually gas-powered for maximum spray force and mobility, though electric models are available for lighter home uses. Whatever the fuel source, the motor’s purpose is to set the water pump in motion and make a cool purring-lion sound.

The pump: When water enters the pressure-washer body from a hose, it passes through a pump that speeds it along into the nozzle. In lower-powered models, this may be an axial pump—akin to a propeller in a tube. Most professional models, however, use piston or plunger pumps with multiple cylinders for increased power. Some pressure-washers can also inject a detergent into the water in the pump to boost its cleansing ability. And systems designed to emit hot water are even more effective.

The wand: Since a garden hose can only supply water so fast, there’s an upper limit on how much a pump alone can increase water pressure. A big part of the pressure boost comes from the rather dainty-looking handheld wand, which constricts water much further than the hose. This constriction forces the water to accelerate, so it emerges from the nozzle at speeds of up to 100 mph. Different nozzle attachments can also change the spray’s shape and size: some focus it into a drill-like spray, while others fan it out to cover large surface areas quickly. Brush attachments may be used for tasks such as cleaning outdoor furniture or turning a chair you left outside all year back into indoor furniture.